Muffler for marine power plants



y 1946- H. w. MONAGHAN MUFFLER FOR MARINE POWER PLANTS Filed Dec. 27 1944 Patented July 23, 1946 MUFFLER FOR MARINE POWER PLANTS Henry W. Monaghan,

New Orleans, La., assignor t0 Higgins Industries, Inc., New Orleans, La., a

corporation of Louisiana Application December 27, 1944, Serial No. 569,961

4 Claims. 1

This invention relates to unsubmerged exhaust mufflers, particularly adapted for marine internal combustion engine power plants.

In general, unsubmerged mufflers have the advantage of being subject to less back pressure than under-Water mufllers, and in shallow draft vessels such as landing craft, it is quite essential that the muffler be above water, to avoid its being torn off when the hull slides over shoals or upon beaches.

Unsubmerged mufflers in general use vary in noise dampenin efliciency with the R. P. M. of the engine. At high speeds they may be acceptably effective, but at low speeds, quite noisy.

The cause of this may be explored by considering the factors which produce noisy exhaust discharge. When the exhaust valve of the engine opens, slugs of hot combustion products under pressure and in potential condition to expand are discharged. In the exhaust pipe these slugs follow one another at close intervals, alternating with intervening regions of exhaust gas of less concentrated heat and pressure. In the absence of a muffler, when the pent slugs reach atmosphere at the end of the exhaust pipe, they suddenly expand, giving an impact blow to the atmosphere, resulting in objectionable staccato noise. At high engine speeds the slugs follow one another at such close intervals as to have the characteristics more or less of a continuous flow and the separateness of the noise impulses is not so keenly detected by the car.

If a simple mufiler, for example, a hollow shell of larger diameter than that of the exhaust pipe and having a tail pipe, is connected to the end of the exhaust pipe, the first slug to enter has room to expand within the shell; therefore, its velocity is checked. Before it has had time to reach the tail pipe, another slug has entered the shell and partially expanded. The effect of the two slugs within the shell at the same time and in different expansion phases is to mix the exhaust products constituting the slugs, so as to destroy their independent slug characteristics, so that the discharge from the tail pipe more nearly approaches a continuous flow. However, when each slug expanded within the shell, it delivered an impact blow against the wall of the shell, the vibrations of which are communicated to the atmosphere.

Under such circumstances there are produced at one and the same time, the noise caused by the expanded issuing jet at the tail pipe and those noises resultant from the knockin of the slugs expanding into the shell, against the wall of the shell. These concurrent noises have different sound characteristics, producing interference, so h t the net effect is a dampening of the objectionable noise of the exhaust.

Much ingenuity and mechanical skill has been devoted to the problem of reducing the impact of the expanding slugs against the shell wall and in reducing the velocity and expansive effect of the issuing jet against atmosphere. The subject invention stems from a scientific study of the causes which produce a noisy exhaust, and by the novel construction and arrangement of parts is believed to have created a more efiicient muffler than those heretofore known.

One of the objects of the invention is to provide a tandem muffler, the forward unit being devoted principally to cushioning the internal shock of the expanding slugs within the shell, and in obliterating the independent slug characteristics of the exhaust, while the posterior unit functions principally to reduce the velocity of the effluent gases, although both units participate to an extent in supplementing the functions of one another.

Another object of the invention is to connect the anterior and posterior units of the muffler by means of a nonmetallic flexible couplin so that vibrations set up in one unit shall not be communicated to and accentuated by the other.

Other objects of the invention will appear as the following description of a preferred and practical embodiment thereof proceeds.

In the drawing Figure l is a perspective view of a mufller embodying the principles of the invention;

Figure 2 is a perspective view of a longitudinal half of the muffler, showing the butterfly valves in place;

Figure 3 is a diametrical section taken along the line 3-3 of Figure 2.

Referring now in detail to the several figures, the numerals l and 2 represent, respectively, the anterior and posterior muffler units which are preferably fabricated by Welding. Figure 2 shows that each unit includes a pipe section, 3 and 4, respectively, which sections are in axial alignment and connected by a flexible, preferably nonmetallic coupling 5.

The pipe sections 3 and. 4 are surrounded by the cylindrical shells 6 and 7, respectively, said pipe sections passing through the respective shells and extending beyond the ends 8 thereof. Said pipe sections lie parallel to the axes of the shells, but offset from said axes so as to define with said shells surrounding chambers which are narrow beneath said pipe sections and capacious above said pipe sections.

Referring now to the anterior unit i, the shell 5 is divided into four compartments I9, 20, 2| and. 22 by a middle imperforate partition 9 and intermediate partitions Ill and H, perforated in that part which lies above the pipe section 3. Said pipe section is provided with four fields of perforations i2, i3, i4 and I5, extending circumferentially thereabout and communicating respectively with the compartments defined by said partitions.

Passage of exhaust gases through the pipe section 3 is controlled by a pair of butterfly valves 56 and ii, mounted on shafts journaled substantially in the planes of the intermediate partitions it and I I. Said valves work together in the same phase, closing and opening together. Said valves are connected by conventional linkage designated" as a whole by the numeral l8, and operated by a rod, (not shown) leading to a point from which it can be conveniently manipulated.

When the butterfly valves are open, the pipe section 3 affords an unrestricted through passage for the exhaust gas. When the butterfly valves are closed, the exhaust gases are by-passed through the shell 6. They first pass through the field of perforations i2 into the shell compartment l9, then through the perforations in the partition it into the shell compartment as, then through the field of perforations l3 into the pipe section 3, then back through the field of perforations I l into the shell compartment 2i, then through the perforations in partition ii into the shell compartment 22, then back into the pipe section 3 through the field of perforations 15. The part of the exhaust gases that pass through those perforations which communicate with the narrow side of the shell chamber are subjected to controlled expansion, since they expand between the divergent walls of the pipe section and shell in the region designated as 23 in Figure 3. The part of the exhaust gases entering the shell through the perforations which communicate with its broad side undergoes relatively uncontrolled expansion into the capacious part of the shell chamber. Thus, turbulence is set up in the shell chamber, effecting a thorough mixing of the exhaust gases, augmented by the mixing which follows the successive direction charges in the serpentine path of travel of the exhaust gases through the shell. This mixing has the eifect of substantially obliterating the independent successive slug characteristics of the exhaust gases, so that the exhaust leaves the pipe section 3 substantially in the form of a continuous flow.

The chamber of the shell 6 always retains some exhaust gas under sub-atmospheric pressure, so

that when the successive slugs of exhaust gas under pressure from the engine blow through the field of perforations l2 into the shell, their impact force is dampened by the gas under pressure already in the shell, so that the shock with which they impinge upon the wall of the shell is dampened to the extent that little or no noise vibrations are communicated through the shell wall to the atmosphere.

Passing now to a description of the posterior unit 2, the pipe section 4 has no cut-off valves,

therefore, it at all times presents a through pas-.

sage for the exhaust gases discharging from the pipe section 3 of the anterior unit. However, the front half of the pipe section 4 is provided at successive longitudinal intervals with the inwardly directed baffles 24, 25, 26 and 21 circumferentially displaced. Forwardly of said baffles the pipe section 4 is formed with the respective fields of perforations 28, 29, 30 and 3|, communicating with the shell B. Each baiiie is designed to apprehend and check the velocity of a portion of the gas traveling through the pipe section 4, and to cause it to pass through the perforations in front of said baffle into the shell I. The bleeding off of part of the gas from the pipe section 4 reduces the volume, and consequently the velocity of the portion remaining in said pipe section, and since the bafiies are spaced apart longitudinally, the reduction in velocity of the gases in the front portion of the pipe section 4 is progressive.

The gases discharged into the shell I suffer turbulence and thorough mixing in the same manner as described in relation to the shell 6, its velocity being further reduced by expansion into the capacious chamber of the shell 1. Any residual slug or impulse characteristics of the exhaust are nullified by the mixing action in the shell 1, and the gases are then returned to the rear portion of the pipe section 4 where their mixture with the jet about to issue from the muffler further homogenizes the exhaust gas in said pipe section, which finally issues in the form of a steady flow at low velocity and without objectionable noise.

In operation, if the engine is running at high speed so that the exhaust impulses follow in such rapid succession as to approach a steady flow, the butterfly valves are opened so that the exhaust gases travel direct through the pipe section 3, without being subjected to preliminary treatment in anterior unit I. They are, however, subjected to the treatment afforded by posterior unit 2. When the engine is running at slower speeds so that there is an appreciable interval between the exhaust impulses, the butterfly valves are closed and the exhaust gases bypassed through the shell 6, being subjected to the noise dampening functions of both units. Anterior unit i can be called into play more or less by adjusting the butterfly valves to intermediate positions. The greater the proportion of the exhaust gases that are passed directly through the pipe section 3, the less will be the back pressure upon the engine.

What I claim as my invention is:

l. Muffler for the exhaust of internal combus tion engines comprising serially connected units, each unit comprising a closed ended shell and a pipe section passing longitudinally through said shell and extending beyond the ends thereof, means connecting the adjacent ends of said pipe section, transverse partitions in one of said shells dividing it into a plurality of compartments, alternate partitions beginning with the most anterior being perforate, the intermediate partition being imperforate, the pipe section which passes through said shell having fields of perforations communicating with the respective compartments, a pair of spaced butterfly valves in said pipe section located substantially in the planes of said perforate portions, means for moving said valves together to obstruct said pipe sections to compel a serpentine flow of exhaust gases through said pipe section and shell, longitudinally spaced and circumferentially displaced baffles in the anterior portions of the other pipe section, fields of perforations in said last named section immediately forward of the respective baflles, and a field of perforations in the posterior portion of said last named pipe section, all of said fields of perforations in said last named pipe section communicating with the shell which sur- 5 rounds it, whereby part of the exhaust gases flowing through said last named pipe section are deflected by said bafiles into said shell through the forward fields of perforations and returned to said last named pipe section through the field 5 of perforations in its posterior portion.

2. Mufiler as claimed in claim 1, the connecting means between said pipe section being a flexible non-metallic coupling.

3. Mufiler as claimed in claim 1, the axes of 10 said shells being ofiset from the axes of the pipe sections which they surround, whereby certain of the intercommunicating perforations open into a narrow part of the shell chambers, while other of said perforations open into a capacious part of said chambers.

4. Muffier as claimed in claim 1, the axes of said shells being offset from and above the axes of the pipe sections which they surround, whereby the lower of the intercommunicating perforations open into a narrow part of the shell chambers while the upper of said perforations open into a capacious part of said chambers.

HENRY W. MONAGHAN. 

